The present invention relates to printer devices, and particularly although not exclusively to a method and apparatus for improving the detection of faulty or clogged nozzles in printer devices.
It is known to produce paper copies, also known as xe2x80x9chardxe2x80x9d copies, of files stored on a host device, e.g. a computer using a printer device. The print media onto which files may be printed includes paper and clear acetates.
Referring to FIG. 1 herein, there is illustrated a conventional host device 100 capable of generating print signals, in this case a personal computer, linked to a printer device 120 via a cable 110. Amongst the known methods for printing text and the like onto a print medium such as paper it is known to build up an image on the paper by spraying droplets of ink from a plurality of nozzles. Printers operating such methods are known as xe2x80x9cink-jet printersxe2x80x9d.
Referring to FIG. 2 herein, there is illustrated schematically part of a prior art ink-jet printer device comprising an array of printer nozzles 220 arranged into a plurality of parallel rows. The unit comprising the arrangement of printer nozzles is known herein as a printer head. In a conventional printer of the type described herein the printer head 210 is constrained to move in a first direction 260 with respect to a print medium 200 e.g. a sheet of A4 paper. In addition, the print medium 200 is also constrained to move in a further, second direction 250 which is preferably substantially orthogonal to the first direction 260. During a normal printing to a print media, printer head 210 is moved into a first position with respect to the print medium 200 and a plurality of ink droplets, e.g., 230 and 240, are sprayed from a same plurality of printer nozzles 220 contained within printer head 210. After the completion of a print operation the printer head 210 is moved in a direction 260 to a second position and another print operation is performed. In a like manner, the printer head is repeatedly moved in a direction 260 across the print medium 200 and a print operation performed after each such movement of the print head 210. When the printer head 210 reaches an edge of the print medium 200, the print medium is moved a short distance in second direction 250, parallel to a main length of the print medium 200, and another print operation is performed. The printer head 210 is then moved in first direction 260 back across the print medium 200 and another print operation is performed. In this manner, a complete printed page is produced, as the print head moves backwards and forwards across the print medium in a direction of travel transverse to the direction of travel of the print medium.
In order to maintain the quality of the printed output of the printer device it is important that each instruction to the printer head to produce an ink drop from a nozzle of the plurality of nozzles does indeed produce such an ink drop. In conventional printers it is known to attempt to detect an ink drop as it leaves the nozzle during a normal print operation. In conventional printers this drop detection is used to indicate the end of life of the printer head 210. Drop detection is known to be performed by a drop detection assembly 270. It is known to locate the drop detection assembly 270 outside of the region used for printing onto the print medium 200 and it is known to locate the drop detection assembly 270 close to an edge of the print medium 200.
U.S. Pat. No. 5,835,108 (Hewlett-Packard) discloses a prior art method and apparatus for detecting and compensating for nozzles or groups of nozzles in print head of an inkjet printer device which mis-direct ink drops on the print media. Mis-directed nozzles are detected by ejecting ink droplets from a first group of nozzles onto a first region of a test pattern and ejecting ink droplets from a second group of nozzles onto a second region of the test pattern. An optical sensor is used to scan across the test pattern in order to detect the positions of the ejected ink droplets on the test pattern.
Since the method disclosed in U.S. Pat. No. 5,835,108 necessitates the use of a scanning device which is mechanically tracked across a special test pattern during a scanning operation, this contributes to the complexity and hence cost of the printing device. Additionally, the scanning operation must require a time substantially longer than the period of time between ejection of ink droplets from a nozzle and the ink droplets striking the print media.
While the presence or absence of an ink droplet fired from a printer head will clearly have an effect on print quality unless it is corrected for, there are other variables which may also have an effect on the quality of the printed output. In particular, variability in the ink droplet volume and deflection of the ink droplet from its true path can result in thin or misplaced lines on the printed page. In art order to optimize print quality it is important to obtain more information regarding the characteristics of an ink droplet fired from a nozzle of a printer head other than simply whether or not a droplet has been fired.
The specific embodiments and methods according to the present invention aim to improve the detection of anomalous nozzles in ink jet printer devices comprising a plurality of nozzles, thereby improving the resulting print quality of such printer devices. Anomalous nozzles may include nozzles which eject a smaller drop volume than expected, or which eject a larger drop volume than expected, nozzles which misfire, nozzles which operate intermittently, and nozzles which are misdirected.
Specific methods according to the present invention, recognize that by comparing a sequence of measurements of an ink droplet ejected from a nozzle near a drop detection device with measurements of ink droplets ejected from adjacent nozzles, misfiring nozzles may be identified and corrected for prior to printing.
According to a first aspect of the present invention, there is provided a method of determining an operating characteristic of a printer head comprising a plurality of nozzles each configured to eject a plurality of droplets of ink, said method comprising the steps of:
detecting a signal resulting from ejection of a predetermined sequence of ink drops from a selected said nozzle;
for each of a set of said plurality of said nozzles, detecting a corresponding respective signal resulting from ejection of a corresponding predetermined sequence of ink drops;
determining a generic signal response from said plurality of detected signal responses of said set of nozzles; and
comparing said detected signal of said selected nozzle with said generic signal determined from said set of nozzles.
Preferably, the method comprises the step of determining a difference between said signal of said selected nozzle and said generic signal determined from said set of nozzles.
According to a second aspect of the present invention, there is provided a method for checking a functionality of at least one selected nozzle of a printer head containing a plurality of nozzles configured to eject droplets of ink, said method comprising the steps of:
sending an instruction to said printer head to eject a predetermined sequence of droplets of ink from said at least one selected nozzle;
generating an output signal from a detecting means configured to detect a passage of said predetermined sequence of droplets of ink past said detecting means; and
applying an algorithm to said output signal to generate an error signal which identifies an anomalous behaviour of said at least one selected nozzle.
Preferably, said predetermined sequence of ink droplets comprises at least one droplet of ink configured such that a total volume of ink of said predetermined at least one droplet lies within a specified range of volume.
Preferably, a total volume of ink contained in said predetermined sequence of droplets is configured to produce an output signal having a substantially larger amplitude than a typical noise amplitude introduced by said detecting means.
Preferably, said predetermined sequence of ink droplets contain a total ink volume substantially within the range 4 picolitres to 100 picolitres.
The method may further comprise the steps of;
for each nozzle of a set of nozzles of said plurality of nozzles, sending an instruction to a print head to eject a predetermined sequence of ink droplets from said nozzle;
for each nozzle of said set, generating a corresponding respective output signal from said detecting means;
wherein said step of applying an algorithm to said output signal comprises the steps of:
determining an average output signal of said detecting means for a plurality of output signals corresponding to said set of nozzles;
calculating a difference between said average output signal and an output signal of said detecting means corresponding to said at least one selected nozzle;
calculating a square of said difference between said average output signal and said output signal of said selected nozzle;
adding said squared difference; and
calculating a positive square root of said summed squared difference.
Said step of applying an algorithm to said output signal may comprise calculating a median output signal from a plurality of output signals corresponding to said set of nozzles.
Said step of applying an algorithm to said output signal may comprise:
finding a maximum value of output signal of said detecting means corresponding to a selected nozzle of said plurality of nozzles;
finding a minimum value of output signal from said detecting means corresponding to said selected nozzle of said plurality of nozzles;
calculating a peak-to-peak difference value between said maximum output signal value and said minimum output signal value of said selected nozzle;
for each of a set of said plurality of nozzles located substantially adjacent said selected nozzle, finding a maximum value of an output signal of said detecting means generated in response to a corresponding respective predetermined sequence of ink droplets ejected from said nozzle, and finding a minimum value of said output signal;
for each nozzle of a said set of nozzles, calculating a respective peak-to-peak output signal value;
calculating an average peak-to-peak value from said plurality of peak-to-peak signal values of said set of nozzles; and
calculating a difference value requesting a difference between said peak-to-peak signal value of said selected nozzle, and said average peak-to-peak signal value of said set of nozzles.
Said step of applying an algorithm to said output signal to detect an anomalous behaviour of at least one nozzle may comprise the steps of:
for each nozzle of a set of said plurality of nozzles which lie adjacent a selected nozzle, generating an output signal in response to a predetermined sequence of ink droplets ejected from said nozzle;
for each generated output signal of said set of nozzles, calculating a first percentile value;
for each said generated output signal of said set of nozzles, calculating a second percentile value;
determining whether an output of said detecting means is greater than said first percentile value or less than said second percentile value;
if said output of said detecting means is less than said second percentile value then calculating a difference value between said output of said detecting means and said second percentile value, and squaring said difference value;
if said output of said detecting means is greater than said first percentile value calculating a difference value between said output of said detecting means and said first percentile value and squaring said difference value;
adding said squared difference values; and
calculating a positive square root of said summed squared difference is values.
Said step of applying an algorithm to said output signal may comprise:
for each nozzle of a set of said plurality of nozzles which lie adjacent a selected nozzle, generating an output signal in response to a predetermined sequence of ink droplets ejected from said nozzle;
differentiating each said output signal of said detecting means for each nozzle of said set of nozzles;
differentiating said output signal obtained in response to said selected nozzle;
calculating an average differentiated output signal from said plurality of differentiated output signals;
calculating a difference between said differentiated output signal of said selected nozzle and said differentiated average output signal;
squaring said difference between said differentiated output signal of said selected nozzle and said differentiated average output signal;
summing said squared difference; and
calculating a positive square root of said summed squared difference.
Said step of applying an algorithm to said output signal may comprise:
for each nozzle of a set of said plurality of nozzles which lie substantially adjacent to said selected nozzle, generating an output signal in response to a predetermined sequence of ink droplets ejected from said nozzle;
differentiating said output signal obtained in response to operation of said selected nozzle;
differentiating each of said output signals obtained in response to ink droplets ejected from said set up of nozzles;
normalising said differentiated output signals of said substantially adjacent nozzles such that said plurality of differentiated output signals have a same peak-to-peak value;
calculating an average differentiated signal from said plurality of normalised differentiated output signals;
calculating a difference between said differentiated output signal of said selected nozzle and said averaged differentiated output signal;
calculating a squared value of said difference;
summing said squared difference; and
calculating a positive square root of said summed, squared difference.
The at least one nozzle may comprise an anomalous nozzle. An anomalous nozzle is characterized by having a malfunction within the set of malfunctions comprising in use, ejecting an ink droplet of a lower than expected ink volume; in use, ejecting an ink droplet of a higher than expected ink volume; in use, operating intermittently; in use, operating unreliably; and in use, ejecting a misdirected ink droplet with deviates from a predetermined trajectory path.
According to a third aspect of the present invention, there is provided a method of determining an operating characteristic of a selected nozzle of an ink jet printer head device comprising a plurality of nozzles, said method comprising the steps of:
obtaining for each nozzle of a set of nozzles, a corresponding respective nozzle signal output from a detecting means configured to detect a passage of at least one droplet of ink ejected from said nozzle;
obtaining for a selected nozzle a selected nozzle signal output from said detecting means;
determining an amount of perturbation of said selected nozzle signal;
obtaining a generic perturbation signal determined from each of said plurality of nozzle signals;
comparing said perturbation signal of said selected nozzle signal with said generic perturbation signal; and
determining whether said selected nozzle corresponding to said selected nozzle signal is operating satisfactorily, based on said comparison of perturbation signals.
According to a fourth aspect of the present invention, there is provided a method of determining an operating characteristic of an ink jet printer head comprising a plurality of nozzles, said method comprising the steps of:
for each said nozzle, ejecting a predetermined sequence of ink droplets;
for a selected said nozzle, generating a corresponding respective perturbation signal having a perturbation produced in response to a said predetermined sequence of ink droplets ejected from said selected nozzle;
from said perturbation signal of said selected nozzle, generating a magnitude signal representing a magnitude of said perturbation;
for each of a set of said nozzles, generating a corresponding respective perturbation signal having a perturbation produced in response to a said predetermined sequence of ink droplets ejected from said nozzle;
generating a generic magnitude signal determined from said plurality of perturbation signals of said set of nozzles; and
for said selected nozzle generating an error signal determined from said corresponding magnitude signal and said generic magnitude signal.
Preferably, said step of generating a magnitude signal comprises performing a plurality of amplitude samples over a plurality of time intervals on said perturbation signal.
Preferably, said plurality of nozzles are arranged in at least one row on said print head, and said generic magnitude signal is determined from a plurality of signal responses corresponding to ink droplets ejected from a plurality of nozzles in a same said row.
Preferably, said plurality of nozzles are arranged in at least one row on said print head, and said generic magnitude signal is determined from signals of a plurality of nozzles of a same row as a said selected nozzle, and extending on each side of said selected nozzle.
Said generic magnitude signal is determined as a median magnitude of said perturbation signals of said set of nozzles.
The invention includes a method of detecting at least one anomalous nozzle of an ink jet printer device comprising a plurality of nozzles arranged substantially in at least one row, said method comprising the steps of:
selecting a nozzle of said plurality of nozzles; and
finding a maximum value of output signal of said detecting means corresponding to a said selected nozzle of said plurality of nozzles;
finding a minimum value of output signal from said detecting means corresponding to said selected nozzle of said plurality of nozzles;
calculating a peak-to-peak difference value between said maximum output signal value and said minimum output signal value of said selected nozzles;
for each of a set of said plurality of nozzles located substantially adjacent said selected nozzle, finding a maximum value of an output signal of said detecting means generated in response to a corresponding respective predetermined sequence of ink droplets ejected from said nozzle, and finding a minimum value of said output signals;
for each nozzle of a said set of nozzles, calculating a respective peak-to-peak output signal value;
calculating an average peak-to-peak signal value from said plurality of peak-to-peak signal values of said set of nozzles; and
calculating a difference between said peak-to-peak signal value of said selected nozzle, and said average peak-to-peak signal value of said set of nozzles.
The invention includes a method of detecting at least one anomalous nozzle of an ink jet printer device comprising a plurality of nozzles arranged substantially in at least one row, said method comprising the steps of:
selecting individual ones of said plurality of nozzles and for each said selected nozzle;
generating an output signal in response to a predetermined sequence of ink droplets ejected from said selected nozzle;
for each generated output signal calculating a first percentile value;
for each said generated output signal calculating a second percentile value;
determining whether an output of said detecting means is greater than said first percentile value or less than said second percentile value;
if said output of said detecting means is less than said second percentile value then calculating a difference value between said output of said detecting means and said second percentile value, and squaring said difference values;
if said output of said detecting means is greater than said first percentile value calculating a difference value between said output of said detecting means and said first percentile value and squaring said difference value;
adding said squared difference values; and
calculating a positive square root of said summed squared difference values.
The invention includes a method of detecting at least one anomalous nozzle of an ink jet printer device comprising a plurality of nozzles arranged substantially in at least one row, said method comprising the steps of:
selecting a said nozzle and generating an output signal in response to a predetermined sequence of ink droplets ejected from said selected nozzle;
for each nozzle of a set of said plurality of nozzles which lie adjacent said selected nozzle, generating an output signal in response to a predetermined sequence of ink droplets ejected from said each nozzle;
differentiating each said output signal of said detecting means for each nozzle of said set of nozzles;
differentiating said output signal obtained in response to said selected nozzle;
calculating an average differentiated output signal from said plurality of differentiated output signals obtained in response to said set of nozzles;
calculating a difference between said differentiated output signal of said selected nozzle and said differentiated average output signal;
squaring said difference between said differentiated output signal of said selected nozzle and said differentiated average output signal;
summing said squared difference; and
calculating a positive square rot of said summed squared difference.
The invention includes a method of detecting at least one anomalous nozzle of an ink jet printer device comprising a plurality of nozzles arranged substantially in at least one row, said method comprising the steps of:
selecting a said nozzle and generating an output signal in response to a predetermined sequence of ink droplets ejected from said selected nozzle;
for each nozzle of a set of said plurality of nozzles which lie adjacent to said selected nozzle, generating an output signal in response to a predetermined sequence of ink droplets ejected from said each nozzle;
differentiating said output signal obtained in response to operation of said selected nozzle;
differentiating output signals of said detecting means obtained in response to said set of nozzles substantially adjacent to said selected nozzle;
normalising said differentiated output signals of said substantially adjacent nozzles such that said plurality of differentiated output signals have a same peak-to-peak value;
calculating an average signal from said normalised, differentiated output signals;
calculating differences between said differentiated output signal of said selected nozzle and said averaged differentiated output signal;
calculating a squared value of each of said differences;
summing said squared differences; and
calculating a positive square root of said summed, squared differences.